CSLB General Building (B)SafetyMedium
A contractor is preparing to dig a trench that will be 6 feet deep in Type C soil. What is the maximum allowable slope for the sides of the trench, according to Cal/OSHA excavation and trenching standards?
- A0.75:1 (53 degrees)
- B2:1 (26.5 degrees)
- C1.5:1 (34 degrees)
- D1:1 (45 degrees)
Show answer & explanationAnswer & explanation
Correct answer: C. 1.5:1 (34 degrees)
For Type C soil, Cal/OSHA requires a maximum allowable slope of 1.5 horizontal to 1 vertical (1.5:1), which corresponds to an angle of 34 degrees from the horizontal.
Why the other options are wrong
- A. A 0.75:1 slope is steeper than allowed for Type C soil and is typically for stable rock.
- B. A 2:1 slope is more conservative than required for Type C soil, but not the maximum allowable.
- D. A 1:1 slope is typically for Type B soil.
Cal/OSHA Trench Slope (Type C)
For Type C soil, Cal/OSHA mandates a maximum allowable slope of 1.5 horizontal to 1 vertical (1.5:1 or 34 degrees from horizontal) for excavations.
- Type C soil is the least stable common soil type.
- Slope must not exceed 1.5:1 (34 degrees).
- This applies to trenches 5 feet or deeper, or when soil conditions warrant.
Memory trick: Alphabetical soils, increasing slope 'A-B-C' for decreasing stability.